An scanning probe microscope (SPM) is a comparatively high-resolution type of scanning probe microscope, with demonstrated resolution of fractions of a nanometer, more than 1000 times better than the optical diffraction limit.
Many known SPMs include a microscale cantilever with a sharp tip (probe) at its end that is used to scan the specimen surface. The cantilever is typically silicon or silicon nitride with a tip radius of curvature on the order of nanometers. When the tip is brought into proximity of a sample surface, forces between the tip and the sample lead to a deflection of the cantilever. One or more of a variety of forces are measured via the deflection of the cantilevered probe tip. These include mechanical forces and electrostatic and magnetostatic forces, to name only a few.
Typically, the deflection of the cantilevered probe tip is measured using a laser spot reflected from the top of the cantilever into a position detector. Other methods that are used include optical interferometry and piezoresistive cantilever sensing.
If the tip were scanned at a constant height tip-sample forces will vary with sample topography, which may cause tip or sample damage, or incorrect topography measurements. As such, in many SPMs a feedback mechanism is employed to adjust the cantilever deflection to maintain a constant force between the tip and the sample. For example, a ‘tripod’ configuration of three piezoelectric crystals may be employed, one for scanning each of the x,y and z directions. This eliminates some of the distortion effects seen with a tube scanner. The resulting map of the area s=f(x,y) represents the topography of the sample.
Regardless of the implementation, after use, the probe tip becomes worn and requires replacement or reconditioning to maintain the accuracy of the SPM. The replacement of the probe tip can be a rather difficult process due to the comparatively small size of the tip and lack of accessibility of the tip in the SPM. Moreover, as noted previously, an optical beam is used to illuminate the probe tip, and the beam is reflected back to a position detector. When a probe tip is replaced in known SPMs, the probe tip is often misaligned relative to the optical beam, necessitating a tedious, labor-intensive procedure to align the tip and beam. The tedium of the alignment process is exacerbated in known SPMs because the process is carried out in-situ. Therefore, significant disadvantages exist in replacing probe tips in many known SPMs.
There is a need, therefore, for a probe tip assembly that overcomes at least the shortcomings of known SPMs discussed above.